Chapter 21
A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?
To the left
Astronomers studying regions like the Orion Giant Molecular Cloud have observed that a wave of star formation can move through them over many millions of years. What sustains such a wave of star formation in a giant molecular cloud?
When massive stars form, their ultraviolet radiation and later their final explosions compress the gas in the cloud and cause a new group of stars to form
Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star?
When nuclear fusion reactions begin inside its core
A Herbig-Haro (HH) object is:
Where a jet from a star in the process of being born collides with (and lights up) a nearby cloud of interstellar matter
A graduate student is given the assignment to find stars with dusty disks around them. What kind of telescope would it be best for her to use for this purpose?
A large telescope that detects infrared radiation
Astronomers call a ball of matter that is contracting to become a star
A protostar
Which of these stars will take the SHORTEST time to go from the earliest protostar stage to the main sequence?
A star ten times the mass of our Sun
Why is it so difficult for astronomers to see new stars in the process of birth?
All of these
If an astronomer wants to find and identify as many stars as possible in a star cluster that has recently formed near the surface of a giant molecular cloud (such as the Trapezium cluster in the Orion Nebula), what instrument would be best for her to use?
An infra-red telescope (and camera)
Planets in the habitable zone of their stars:
Are at a temperature where water can exist as a liquid
When astronomers carefully examine the planets found by Kepler and draw conclusions from the Kepler sample, what do they conclude about planets the size of Earth?
Earth-sized planets are common, but so are planets somewhat bigger than Earth
The star now called Kepler-444 is 11 billion years old (much older than the Sun) and has five planets orbiting close to it. What has this system taught astronomers about the history of star formation?
If such an old star has planets close to it, where it's really warm, those planets must be made of heavier elements. So heavier elements must have formed before the time this star formed.
If you want to find stars that are just being born, where are the best places to search?
In giant molecular clouds
When a star settles down to a stable existence as a main-sequence star, what characteristics determines where on the main sequence in an H-R diagram the star will fall?
Its mass
Astronomers believe that disks of material will form around protostars that are spinning. Which of the following observed phenomena is a good indication of the presence of a disk around a protostar?
Jets and Herbig-Haro objects
In figuring out the evolutionary tracks on the H-R diagram, astronomers:
Make model stars on a computer and then follow how their characteristics will change with time
What technique did astronomers use to make the first confirmed discovery of a planet around another star like the Sun?
Measure the Doppler shift of the lines in the star's spectrum and look for periodic changes in this shift due to the pull of the planet as it orbits the star
Astronomers were surprised to find so many Jupiter-mass planets so close to their stars. According to their best theories and models, such "hot Jupiters":
Must have formed further out from the star and must have "migrated inward" early on
The big surprise about the first planet discovered around another regular star was that it:
Orbited so close to its star it took only 4 days to go around
Which of the following is NOT one of the reasons planets around other stars are so difficult to detect?
Planets only form very late in the life of a star, just when it is ready to die, and thus last only a very short fraction of the star's life
Why was the Kepler mission not able to find planets smaller than Mars, even though it was in space (and had no Earth atmosphere to deal with)?
Such planets make dips in the light of the star that are too small for Kepler to detect
Which of the following are the small regions that are the embryos of stars (where individual stars are most likely to be born)?
The cores within the clumps of molecular clouds
What observations about disks of dusty material around young stars suggest that planets may be forming in such disks?
The disks show lanes that are empty of dust within them
